This invention relates in general to a method for treating a preformed flexible imaging member belt to substantially eliminate ripples from the belt.
Coated flexible belts or tubes are employed extensively in various arts. They are, for example, commonly utilized for numerous purposes such as electrostatographic imaging members, which include electrophotographic imaging members and electrographic imaging members.
Flexible electrostatographic imaging members, e.g. belts, are well known in the art. Typical electrostatographic flexible imaging members include, for example, photoreceptors (i.e. electrophotographic imaging members) for electrophotographic imaging systems and electroreceptors (e.g. ionographic imaging members) for electrographic imaging systems. Though both electrophotographic and ionographic imaging members are commonly utilized in either a belt or a drum configuration, nevertheless, the belt configuration is generally preferred based on cost and flexibility of machine design considerations. These electrostatographic imaging member belts may be seamless or seamed. Although the present invention encompasses both electrographic and electrophotographic imaging members, the discussion hereinafter will focus mainly on electrophotographic imaging members for reasons of simplicity.
For electrophotographic applications, the imaging member belts often comprise a flexible biaxially oriented thermoplastic supporting substrate coated with one or more layers including at least one layer of photoconductive material. The substrates may be inorganic such as electroformed nickel or organic such as a film forming polymer. The photoconductive coatings applied to these belts may be inorganic such as selenium or selenium alloys or organic. The organic photoconductive layers may comprise, for example, single binder layer in which photoconductive particles are dispersed in a film forming binder or multilayers comprising, for example, a charge generating layer and a charge transport layer.
Electrophotographic imaging members having a belt configuration are normally entrained around and supported by at least two rollers. Generally, one of the rollers is driven by a motor to transport the belt around the rollers during electrophotographic imaging cycles. Since electrophotographic imaging belts, particularly welded seam belts, are not perfectly cylindrical and, more specifically, tend to be slightly cone shaped, these flexible belts tend to "walk" axially along the support rollers. Belt walking causes one edge of the belt to strike one or more edge guides positioned adjacent the ends of the rollers to limit axial movement. Friction between the edge guide and the edge of the electrophotographic imaging member belt can cause the belt edge to wear, rip, buckle and otherwise damage the belt. Also, there are other serious drawbacks in terms of belt tracking and problems with good image registration. Welded belts, because of the difficulties associated with perfectly aligning overlapping ends during seam welding, are not is as concentric as desired.
Moreover, an imaging member belt fabricated by overlapping the opposite ends of an imaging member sheet and ultrasonically welding the overlapped ends to form a welded seam belt has always been observed to give rise to ripples formation near either side of the welded seam. Cross sections of these ripples exhibit a sinewave pattern which traverses across the entire width of the belt. Typical ripples seen in a seamed belt have a peak to peak height of between about 400 micrometers and about 500 micrometers and with a wavelength of from about 35 to about 45 millimeters. These ripples are clearly visible to the naked eye. Since the ripples undesirably alter the often critical distances between the belt imaging surface and devices such as optical exposure means, charging corotrons, developer applicators, transfer stations and the like, the ripples adversely affect copy print quality and are manifested as print-out defects.
Another type of electrophotographic imaging member that is well known in the art are drum type photoreceptors. Some drum photoreceptors are coated with one or more coatings. Coatings may be applied by well known techniques such as dip coating or spray coating. Dip coating of drums usually involves immersing of a cylindrical drum while the axis of the drum is maintained in a vertical alignment during the entire coating and subsequent drying operations. Although the drum photoreceptors have the benefit of being very dimensionally precise than the belt photoreceptor counterparts, yet they do have an inherent coating layer shortfall due to the vertical alignment of the drum axis during the coating operation, the applied coatings tend to be thicker at the lower end of the drum relative to the upper end of the drum due to the influence of gravity on the flow of the coating material. Drum coatings applied by spray coating technique can also be uneven, e.g., the well known orange peel effect. Coatings that have an uneven thickness do not have uniform electrical properties at different locations of the coating. Also, the coating of drums in a batch operation is time consuming and costly. In addition, the many handling steps required for batch drum coating processes tend to increase the likelihood that one or more coatings will be damaged or contaminated. Although the drum photoreceptor configuration produces excellent precise dimensions compared to belt photoreceptors, dip or spray coated photoreceptor drums do not exhibit the superior electrophotographic characteristics of flexible electrostatographic imaging belts. Moreover, the coatings are difficult to remove without damaging the underlying drum during reclaiming operations thereby rendering the drum less suitable for recycling.